Burr mill



March 25, 1958 F. E. KNOEDLER BURR MILL 3 Sheets-Sheet 1 Filed Aug. 22, 1955 F. E. KNOEDLER March 25, 1958 BURR MILL 3 Sheets-Sheet 3 Filed Aug. 22, 1955 United States BURR MILL Application August 22, 1955, Serial No. 529,874

9 Claims. (Cl. 241-162) The present invention relates to burr mills and particularly to burr mills for grinding wheat, oats, barley and other small grains.

There are -in-use today burr mills which are specifically designed 'to grind unshelled corn on cobs, shelled corn or cobs at a high rate. When it is attempted to grind small grains such as wheat, oats, barley and the like with these burr mills, unsatisfactory results are obtained. If the rate of grind is adjusted so that the material being ground is not heated up and burned, the rate of grind is too low for modern day usage. If, on the other hand, the rate of grind is increased to a practical rate, the material being ground is heated up and in some cases burned which makes the ground feed less desirable.

Accordingly, it is an object of the present invention to provide an improved burr mill which can grind wheat, oats, barley and similar small grains at high rates without heating up and burning the ground material.

Another object of the invention is to provide in a burr mill of the type set forth, grinding members and mounting therefor which are particularly adapted and suited to grind wheat, oats, barley and similar small grains at highrates without burning. y

In connection with the foregoing object, it is another object of the invention to provide an assembly of grinding members and mounting therefor which can be readily interchanged with grinding members adapted to grind unshelled corn and the like in the same burr mill.

Yet another object of the invention is to provide a burr mill for grinding small grains having an improved system of grinding members including a plurality of stationary burrs having a plurality of rotating burrs disposed between alternate stationary burrs to provide parallel grinding areas to which material to be ground is fed in parallelisrn.

Still another object of the invention is to provide an improved adjustable mounting for grinding members of the type set forth in which the pressure exerted by the grinding members upon grain positioned therehetween can be readily adjusted.

These and other objects and advantages of the invention will be better understood from the following description when taken in conjunction with the accompanying drawings. In the drawings wherein like reference numerals have been utilized to designate like parts throughout:

Figure 1 is a partial view in vertical section with certain parts broken away of a burr mill made in accordance with and embodying the principles of the present invention;

Figure 2 is an enlarged partial view in vertical section showing the grinding members and the mounting therefor in operative position;

Figure 3 is an exploded view of certain parts illustrated in Figure 2;

Figure 4 is also an exploded view of certain of the parts illustrated in Figure 2, the parts of Figure 3 being asatent sembled on top of'the parts of Figure 4 in operative position; and

Figure 5 is a fragmentary view showing a modification of a burr mill made in accordance with the present invention and utilizing three stationary burrs and two ro tatin g burrs.

There is shown in Figure 1 of the drawings a bunmill generally designated'by the numeral 10 made in accordance with and incorporating the principles of the present invention. Mill 10 includes a base 12 from which rise a plurality of walls including circular wall 14 and wall 16. Mounted upon wall 14 is a casting 20 which in turn supports a bowl 22. Material to be ground is fed downwardly through a 'hopper24 which rests upon and is supported by bowl 22. Ground material is removed from mill 10 by an elevator generally designated by the numeral 26 which connects with a discharge spout 23.

The power to drive mill 10 is derived from a tractor or other suitable prime mover and is supplied to mill 10 by means of a drive shaft 3t). Drive shaft 30 is supported by aball bearing assembly 32 suitably mounted upon wall 16 by nuts and bolts 34. Shaft 30 is further supported by another ball bearing assembly 36 mounted upon wall 18. The inner end of shaft 30 carries a bevel gear 38 which meshes with a larger bevel gear 40. Gear 40 is mounted upon and drives a vertically disposed shaft 42.

The lower end of shaft 42 is supported by a bridge tree :44 which is mounted in a pivotal manner upon a block 46 at one end and supported by an attached rod 48 at the other end. Rod 48 passes through an eye 50 on a rod 52 and rod 52 passes upwardly to be engaged by a pair or" handwheels 54. A spring 56 is disposed about rod 52 and the lower end thereof rests upon the topside of a housing 58. The underside of the lower handwheel 54 engages a sleeve 60 which also surrounds rod 52 and bears against the upper end of spring 56. By turning .handwheels 54 with respect to rod 52, the bridge tree 44 can be lifted whereby to lift shaft 42 with respect to base 12 for adjustment purposes more fully explained hereinafter.

Mounted upon base 12 and surrounding shafts 42 is a ball bearing assembly 62 supported by a frame 63. A second ball bearing assembly 64 is provided about shaft 42 and is bolted to the underside of casting 20 by nuts and bolts 66.

Casting 20 which serves as the grinding chamber is circular and is provided with a bottom 68 to which the ball bearing assembly 64 is bolted as described above and an upstanding cylindrical wall 70. Wall 70 is provided with an inwardly disposed shoulder 72 (see Figure 2) upon which rests a lower burr 74. Disposed above burr 74 is a two faced rotating burr 76 and disposed above the upper face of burr 76 is a third burr 78 which is stationary during operation. The two stationary burrs 74 and 76 are maintained in their stationary positions with respect to casting 2% by a retainer ring 80 which is substantially.cylindrical in shape. Equally spaced about the inner periphery of ring 89 are four legs 82 which are rectangular inshape and extend fromthe upper edge of ring 80 beyond the lower edge of ring 80. The lower ends of legs 82 are adapted to fit in apertures provided along the shoulder 72 of wall 70 whereby to maintain ring 80 stationary with respect to casting 20. The lowermost burr 74 has a generally circular outline in which four rectangular notches 84 (see Figure 4) are provided to re ceive and coact with legs 82. This thereby serves to'hold the lower burr 74 stationary with respect to casting 20. The upper stationary burr 78 is provided with four out wardly extending shoulders 86 which also interfit with legs 82 whereby to prevent burr 78 from rotatingwith re 3 spect to casting 20 yet permit burr 78 to be moved and adjusted in a vertical direction.

The rotating burr 76 is driven from the vertical shaft 42. More specifically, shaft 42 carries at its upper end a drive member generally designated by the numeral 88 which serves to interact with and drive burr 76. Member 88 includes a cylindrical portion 90 which is apertured to receive the upper end of shaft 42. The extreme end of shaft 42 is cut away to provide shoulder 92 which reacts against projections 94 formed within member 88. Extending outwardly from the lower end of cylindrical portion 90 is a plurality of curved arms 96 which are adapted to engage members on burr 76 whereby to impart movement to burr 76.

. Referring to Figures 2 and 4, burr 74 is formed substantially flat along its lower side as has been explained above and is substantially circular in shape. It is supported upon the shoulder 72 by four outwardly directed projections 98 in which are formed the notches 84. The recessed sides 100 between projections 98 are disposed radially inwardly from the inner periphery of wall 70 whereby to permit ground material to fall between sides 100 and wall 70 to the bottom 68 of casting 20. Disposed inwardly from sides 100 are a plurality of grinding surfaces 162 which coact with the lower grinding surfaces on burr 76 to effect the grinding operation. A circular aperture 104 is formed in the center of burr 74. Formed on the upper surface of burr 74 is a plurality of guide vanes 186 which guide and direct material to be ground outwardly toward the grinding surfaces 102.

The movable burr 76 is also formed as a substantially flat circular plate and is provided on both sides thereof with a plurality of upper grinding surfaces 108 and lower grinding surfaces 109. A plurality of guide vanes 110 serve to aid in guiding the material to be ground toward the grinding surfaces. Formed as continuations of the guide vanes 110 are projections 112 which extend into a generally circular aperture 114 in the center of burr 76. Alternate projections 112 coact with the arms 96 on drive member 88 to provide means for rotating the burr 76. Formed on the outer periphery of burr 76 and extending outwardly therefrom is a plurality of projections 116 which serve to clear ground material from the area on top of projections 98 on burr 74 and below the projections which carry the shoulders 86 on the upper burr 78. This is necessary because the outer periphery of burr 76 has the same diameter as the circle of which sides 100 on burr 74 are segments.

The upper burr 78 is provided with projections 118 on which are formed the shoulders 86 referred to above. Grinding surfaces 120 are formed on the lower side of burr 78 (see Figure 2) and coact with the grinding surfaces 108 on the upper side of the moving burr 76. A plurality of guide vanes 122 are also provided on the lower surface of burr 78 to guide the grain to be ground to grinding surfaces 120. The upper surface of burr 78 has an inner groove 124 formed therein concentric with the center of burr 78 and a second concentric groove 126 concentric with groove 124. In addition, a pair of recesses 128 and 130 are formed in the upper surfaces of burr 78.

The top burr 78 is controlled as to vertical movement by a pressure distributing member or tripod generally designated by the numeral 132 and a bridge generally designated by the numeral 134. Tripod 132 includes a flat ring 136 which is shaped to fit within the groove 124 on the upper surface of burr 78. Extending upwardly from ring 136 are three legs 138 which support a generally triangular plate 140. Mounted in substantially the center of plate 140 is an upstanding cylindrical lug 142 which serves to hold a compression spring 144 in operative position thereon.

Bridge 1134 is adapted to straddle tripod 132. Bridge 134 includes a pair of angularly disposed legs 146 and moved up and down with respect to plate 154.

148 provided at their lower ends with outwardly directed feet 150 and 152, respectively, and are connected at their upper ends by a plate 154. The feet 150 and 152 are adapted to be disposed in recesses 12S and 130 of burr 78 and notches 153 formed in ring 136. Plate 154 is apertured whereby to receive a threaded rod 156, the lower end of which carries a plate 158 engaging the upper end of spring 144. A threaded nut 159 is secured as by welding to plate 154 to support rod 156. The upper end of threaded rod 156 has a handwheel 160 fixedly attached thereto whereby to permit rod 156 to be turned and Movement of rod 156 with respect to plate 154 tends to increase or decrease the compression of spring 144.

Referring now particularly to Figure 2, the construction and mounting of bowl 22 will be described in detail. Bowl 22 is shaped as a section of a cone inverted whereby to provide a widened opening at the top converging to a narrower opening at the bottom. Suitably secured to the bottom edge of bowl 22 is an outwardly extending flange 164 which is adapted to engage against the upper surface of feet l50152 of the bridge 134. A second outwardly directed flange 166 is welded to bowl 22 above flange 164 and is positioned to engage the upper edge of casting wall 70. A hinge and a clamp (not shown) interconnect the bowl 22 and the casing 20 to press the flange 166 firmly against the upper edge of the casting wall 70. The upper edge of bowl 22 has a third flange 168 extending therearound and outwardly therefrom to serve as a means for attaching the hopper 24 (see Figure 1). Hopper 24 is provided at its lower end with a casting 170 which carries a plurality of handwheel attachment assemblies 172 which serve to connect hopper 24 to bowl 22 by engaging flange 168.

Grain to be ground is placed in hopper 24 and falls downwardly to bowl 22 from which it passes to the burrs More specifically, grain follows a pair of parallel paths through the burrs. The first or upper path is between grinding surfaces on burr 78 and upper grinding surfaces 108 on burr 76. The second is between the lower grinding surfaces 109 on burr 76 and grinding surfaces 102 on burr 74. Because of the apertures in the centers of the various burrs, grain is free to fiow simultaneously to these two grinding areas. In addition, the various guide vanes 106, 110 and 122 aid in directing the grain in an outward direction and into these two grinding areas. The ground grain passes outwardly beyond the periphery of the movable burr 76 and falls down between sides 100 of burr 74- and wall 70 of casting 20. More specifically, the ground material falls upon the bottom 68 of casting 20.

Means is provided to remove the ground material from within casting 70 in the form of a paddle wheel generally designated by the numeral 174 which pushes the ground material outwardly through an aperture 175 in wall 70 and into a receiving chamber 176. Paddle wheel 174 includes a substantially circular plate 178 on which are integrally formed five paddles 180. Paddles 180 extend from bottom 60 of casting 20 to the under side of burr 74 as can be best seen in Figure 2. The center of plate 178 is thickened as at 182 and is apertured as at 184 to receive the drive shaft 42. A key 186 (see Figure 4) connects paddle wheel 174 to shaft 42. Each paddle blade 180 is also provided with a rectangular notch 188 in the lower edge thereof to clear the bolts 66.

It will be seen from the above description that rotation of shaft 42 causes rotation of paddle wheel 174. This moves the ground material into the receiving chamber 176. The ground material is picked up in chamber 176 by a screw 190 which serves to lift it upwardly. The lower end of a shaft 192 which carries screw 190 is journaled and supported by a ball bearing assembly 194. Attached to the lowermost end of shaft 192 is bevel gear 196 which meshes with a second bevel gear 198 on the assess? main drive shaft 30. Power derived from shaft 30 is thereby used to turn shaft 192.

Mounted upon chamber 176 is a cylindricalhousing 200 surrounding screw 190. The lower end of housing 200 has fixed thereto an outwardly directed flange 201 which is rotatably restrained by ring .202 mounted on the housing for chamber .176. This permits housing 200 to be rotated about its axis. The upper end of shaft 192 is received and rotativel y operated by abearing 204 on the upper end of housing 260. The discharge spout 28 is pivotally attached to the housing 200. .A clamp mechanism generally designated by number 206 and mounted onbowl 22 serves to lock housing 200 in any desired position withrespect to bowl 22. If it is desired to change the direction of spout 23 the clamp mechanism 206 is loosened whereby to permit housing 200 to be rotated with respect to bowl 22. When the desired position is obtained, the clamp mechanism 206 is then tightened.

Referring now particularly to Figures 1 and 2 of the drawings, the operation of the burr mill will be described in detail. The main drive shaft 30 is attached to a tractor or other suitable source of motive power whereby to turn vertical shaft 42 and elevator shaft 192. The vertical position of shaft 42 is then adjusted by means of the handwheels 54. More specifically, it is desired to adjust the vertical position of drive member 88. There is provided above paddle Wheel 174- and carried by burr 74 a plate 208 which is apertured as at 210 to receive shaft 42. The diameter of plate 208 is slightly greater than the diameter of aperture 104 in burr 74 whereby to support plate 208 on a shoulder provided between the ends of vanes 106 and the edge of aperture 104. Plate 208 serves the purpose of preventing grain that has not been ground from passing between burr 74 and plate 178 onto bottom 68. It is necessary to position shaft 42 in the proper place vertically so that the necessary clearanceis given between the lower edge of drive member 88 and tightened by locking the handwheels 54, the pressure exerted by tripod member 132 against burrs 76 and 78 is adjusted by turning the handwheel 160. Next, grain or other material to be ground is dumped into hopper 24. :Preferably, for convenience sake, a continuous feed of material to hopper 24 is provided.

The grain falls into bowl 22 and is directed into the grinding areas. The pressure exerted upon the grain between the grinding surfaces, i. e., between grinding surface 120 and the upper grinding surface 108 and between the lower grinding surface 109 and grinding surface 162 determines the size or fineness of grind. The greater the pressure the finer the grind and, vice versa, the smaller the pressure the coarser the grind. The grain is fed simultaneously to the two sets of grinding surfaces and is completely ground to the desired degree of fineness 'by a single pass through one of the grinding areas. The grain enters the grinding areas in the centers of the burrs and passes outwardly to the outer edges of the burrs as it is ground. The ground grain falls downwardly past the periphery of moving burr 76 and between sides 100 of burr 74 and wall 70 of casting 20.

The paddle wheel 174 then moves the ground material into the receiving chamber 176 where it is picked up by screw 190. Screw 190 lifts the ground material upwardly through housing 200 and discharges it into spout 28. Spout 28 in turn discharges the ground material at the desired point.

Referring now to Figure 2, the adjustment of the burrs to adjust the degree of fineness will be described in greater detail. The movable burr 76 and the upper stationary burr 78 are free to move or float in a vertical direction above the lower stationary burr 74. If a large amount of grain is forced between the burrs, the presence of the grain tends to lift burrs 76 and 78 upwardly thereby increasing the distance between the grinding surfaces.

In order to control the pressure exerted upon grain positioned between .the grinding surfaces, the "tripod 3132 and the bridge 134 are provided. The feet -.152 of bridge .134 are engaged beneath the flange 164 of bowl 22. Since bowl 22 is fixedto the remainder of the machine, bridge 134 is held immovable. The ring 136 of tripod 132 rests upon and bears against the upper stationary burr 78. Spring 144 acting against bridge 134 forces tripod 132 downwardly against the upper burr 78. By increasing the pressure exerted by spring 144 against tripod 132, the fineness of grind can be increased. The compression of spring 144 and therefore the downward pressure exerted on tripod .132 can be adjusted by turning handwheel lfitl. When plate 158 is moved downwardly from plate 154 to compress spring 144, the pressure on tripod 132 and therefore the pressure on grain between burrs 76and 78 and between burrs '74 and 76 is increased.

If it is desired to replace burrs 747678 with new burrs or with a different set of burrs, this can be readily done in the following manner. The bowl 22 is released (by removing a bolt not Shown) and then swung back and down on a hinge (not shown). Tripod 132 and bridge 134 can then be lifted out and off of burr '78. The burrs themselves and the drive member 88 can then be lifted upwardly and removed from shaft 42. Shaft 42 can then receive a new set of burrs or a different set of burrs if desired. Bowl 22 is then swung back into position, the burrs adjusted, and the machine is ready to grind again. By providing the mounting and adjustment -illustrated in the drawings, and by providing the paratlel paths of grinding, small grains such as wheat, oats and barley can be ground at a rapid rate. Rapid grinding is obtained without burning or scorching the grain. Accordingly, a good-tasting product is assured. The arrangement also provides for a uniform and adjustable fineness of grind.

There is shown in Figure 5 a modification of the present invention in which three stationary burrs are utilized with two rotating burrs. An upstanding wall 22b similar to wall 72 is provided having shoulder 222 adapted to receive a support ring 224 similar in construction to ring 80. Ring 224 is provided with four legs 226 received in notches formed in wall 220. A lowermost burr 228 substantially identical with burr 74 is provided. A set of grinding surfaces 230 are formed on burr 223 and cooperate with a set of grinding surfaces 232 on a retating burr 234.

Burr 234 is substantially identical to burr 76 and is provided with a second upper grinding surface 236.

An intermediate stationary burr 238 is provided and interlocks with legs 226. A lower grinding surface 240 and an upper grinding surface 242 are provided upon burr 238. A second rotating burr 244 having grinding surfaces 246 and 248 is mounted above stationary burr 238. A third and topmost stationary burr 250 having a lower grinding surface 252 is provided to complete the assembly of grinding burrs.

A tripod similar to tripod 132 and including a ring is provided to overlie burr 250 so that the pressure exerted by the burrs against grain positioned between the burrs can be adjusted. To this end a bridge 256 is provided which is similar to bridge 134 described above. Bridge 256 is adapted to interact with a bowl 258 having flanges 260 and 262 which perform the same function as flanges 164 and 166 explained above.

The movable burrs 234 and 244 are driven by a drive member similar to drive member 88 except that the arms 96 are made sufficiently thick to engage both burrs 234 and 244 at the same time. Grain to be ground flows between opposed sets of grinding surfaces whereby to grind the grain.

It will be seen that an even larger number of stationary and rotating burrs can be employed if desired pro- *vided that sufiicient power to drive the rotating burrs is supplied. The fineness of grind in these alternative constructions is also adjusted by adjusting the pressure exerted by the burrs against grain flowing between opposed grinding surfaces of the burrs.

spirit and scope thereof. Accordingly, the invention is to be limited only as set forth in the following claims.

I claim:

1. A burr mill comprising a wall defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from the bottom of said grinding chamber, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr non-rotatably, a second burr having a horizontal grinding surface and mounted above said first burr within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted be tween said first and second burrs and having horizontally disposed grinding surfaces co-acting with the grinding surfaces on said first and second burrs, means to drive said third burr, and resilient means urging said second burr toward said third burr and said first hurr.

2. A burr mill comprising a wall defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from the bottom of said grinding chamber, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr non-rotatably, a second burr having a horizontal grind ing surface and mounted above said first burr Within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having horizontally dis-- posed grinding surfaces co-acting with the grinding surfaces on said first and second burrs, means to drive said third burr, resilient means urging said second burr toward said third burr and said first burr, and means to vary the pressure exerted by said resilient means to vary the degree of fineness of the ground material.

3. A burr mill comprising a wall and an integral horizontally disposed bottom member defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from said bottom member, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr nonuotatably, a second burr having a horizontal grinding surface and mounted above said first burr within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and surfaces co-acting with the grinding surfaces on said asaaosv first and second burrs, means to drive said third burr, a bridge member overlying said second burr and being substantially immovable in an upward direction with respect to said wall, a pressure distributing member resting upon said second burr, and a spring disposed between said bridge member and said pressure distributing member urging said pressure distributing member and said second burr toward said third burr and said first burr.

4. A burr mill comprising a wall and an integral horizontally disposed bottom member defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from said bottom member, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr non-rotatably, a second burr having a horizontal grinding surface and mounted above said first burr within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having horizontally disposed grinding surfaces co-acting with the grinding surfaces on said first and second burrs, said burrs having aligned apertures in the center thereof, means to feed material to be ground into the apertures in said second and third burrs and outwardly between each adjacent set of grinding surfaces to grind the material as it moves to the periphery thereof, the bottom member and the area beneath said first burr forming a depository for ground material, a paddle member mounted to sweep material from said depository, means to drive said third burr and said paddle member, and resilient means urging said second burr toward said third burr and said first burr to regulate the degree of fineness of the ground material.

5. A burr mill comprising a Wall and an integral horizontally disposed bottom member defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from said bottom member, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grindin surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr nonrotatably, a second burr having a horizontal grinding surface and mounted above said first burr within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having horizontally disposed grinding surfaces co-acting with the grinding surfaces on said first: and second burrs, said burrs having aligned apertures formed centrally thereof, means to feed material to be ground into the apertures in said second and third burrs and outwardly between each adjacent set of grinding surfaces to grind the material as it moves to the periphery thereof, a drive shaft extending vertically upwardly through an aperture in said bottom member and through the apertures in said burrs, a drive member non-rotatably mounted upon said drive shaft, said drive member engaging said third burr positively in a horizontal direction and slidably in a vertical direction, and means resiliently to urge said second burr toward said third burr and said first burr to regulate the degree of fineness or the ground material.

6. A burr mill comprising a wall and an integral horizontally disposed bottom member defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from said bottom member, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr non-rotatably, a second burr having a horizontal grinding surface and mounted above said first burr within said grinding chamber and movable vertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having horizontally disposed grinding surfaces coacting with the grinding surfaces on said first and second burrs, said burrs having aligned apertures formed centrally thereof, means to feed material to be ground into the apertures in said second and third burrs and outwardly between each adjacent set of grinding surfaces to grind the material as it moves to the periphery thereof, a drive shaft extending vertically upwardly through an aperture in said bottom member and through the apertures in said burrs, a drive member nonrotatably mounted upon said drive shaft, said drive member engaging said third burr positively in a horizontal direction and slidably in a vertical direction, a paddle member disposed between said first burr and said bottom member and drivingly connected to said drive shaft, a plate loosely resting upon said first burr and filling the aperture in said first burr, and means resiliently to urge said second burr toward said third burr and said first burr to regulate the degree of fineness of the ground material.

7. A burr mill comprising a wall defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from one end of said grinding chamber, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr non rotatably, a second burr having a grinding surface and mounted within said grinding chamber and spaced from said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having grinding surfaces co-active with the grinding surfaces on said first and second burrs, means to drive said third burr, and resilient means urging said second burr toward said third burr and said first burr.

8. A burr mill comprising a wall defining a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring mounted on said shoulder and spaced from one end of said grinding chamber, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a grinding surface mounted upon and supported by said shoulder and having portions engaging said retainer members to mount said first burr nonrotatably, a second burr having a grinding surface and mounted within said grinding chamber and spaced from said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted be? tween said first and second burrs and having grinding surfaces co-active with the grinding surfaces on said first and second burrs, said second and third burrs having apertures in the center thereof, means to feed the ma terial to be ground into the apertures in said second and third burrs and outwardly between each adjacent set of grinding surfaces to grind the material as it moves to the periphery thereof, means to drive said third burr, and resilient means urging said second burr toward said third burr and said first burr.

9. A burr mill comprising a wall defining: a grinding chamber, a shoulder formed on the inner periphery of said wall, a ring rnounted on said shoulder and spaced from the bottom of said grinding chamber, retainer members mounted on said ring and engaging said wall to hold said ring non-rotatably with respect to said wall, a first burr having a horizontal grinding surface mounted upon and supported by said shoulder and having por tions engaging said retainer members to mount said first burr non-rotatably, a second burr having a. horizontal grinding surface and mounted above said first burr within said grinding chamber and movable ertically above said first burr, projections formed on said second burr engaging said retainer members to prevent rotation of said second burr, a third burr rotatably mounted between said first and second burrs and having horizontally disposed grinding surfaces co-acting with the grinding surfaces on said first and second burrs, said second and third burrs having apertures in the center thereof, means to feed the material to be ground into the apertures in said second and third burrs and outwardly between each adjacent set of grinding surfaces to grind the material as it moves to the periphery thereof, means to drive said third burr, and resilient means urging said second burr toward said third burr and said fu'st burr.

References Cited in the file of this patent UNITED STATES PATENTS 295,049 Raymond Mar. 11, 1884 1,002,419 McCargar Sept. 5, 1911 1,063,810 Lyon June 3, 1913 1,135,017 Hiller Apr. 13, 1915 1,329,741 Bausman Feb. 3, 1920 1,409,238 Punteney Mar. 14, 1922 2,176,892 Dotzer Oct. 24, 1939 2,356,753 Dotzer Aug. 29, 1944 2,432,610 Dryer Dec. 16, 1947 

